This application is based upon, claims the benefit of priority of, and incorporates by reference the contents of prior Japanese Patent Application No. 2002-49681 filed Feb. 26, 2002.
1. Field of the Invention
The present invention relates to an electromagnetic clutch that transmits and terminates rotational power, and particularly, the present invention relates to a reduction in clutch operating noise generated when the electromagnetic clutch actuates and stops.
2. Description of Related Art
One type of known electromagnetic clutch is disclosed in Japanese Patent Laid-Open Publication No. 2000-179582. The patent application is composed of an armature attracted to a drive-side rotation member by an electromagnetic force generated by an electromagnetic coil, a driven-side rotation member connected to a driven-side rotation device, and a plate of ring-shaped leaf springs, as a spring means, connecting the armature to the driven-side rotation member.
The ring-shaped leaf spring comprises an outer ring portion connected to the armature, an attachment portion disposed inside the outer ring portion and connected to the driven-side rotation member, connecting portions connecting between the outer ring portion and the attachment portion, securing portions of the armature disposed in a plurality of positions of the outer ring portion in a circumferential direction, and a deflection adding portion for providing an initial deflection to the ring-shaped leaf spring. The deflection adding portion is arranged between the plural positions of the outer ring portion in the circumferential direction so that it acts to shorten an axial dimension of the electromagnetic clutch and to simplify the overall configuration.
Using the ring-shaped leaf spring in the above-mentioned configuration, since a spring force which increases non-linearly and rapidly relative to a displacement amount of the armature restricts movement of the armature just before the armature collides with the drive-side rotation member, a collision force of the armature with the drive-side rotation member is reduced to reduce the operating noise of the electromagnetic clutch.
In order to further reduce the operating noise of the electromagnetic clutch, there is an extending portion inwardly extending an arm portion, which is a securing portion disposed in the outer ring portion of the ring-shaped leaf spring to secure the leaf spring to the armature, and an elastic member disposed in an opposite position to the extending portion of the arm portion. Thus, when the electromagnetic clutch is ON, that is, when the electromagnetic force generated by the electromagnetic coil attracts the armature toward the drive-side rotation member, the elastic member is elastically compressed in a relative fashion to increase a displacement amount of the arm portion, so that the elastic member alleviates an impact of attraction of the armature to the drive-side rotation member and further reduces the clutch operating noise.
The above-mentioned leaf spring functions as a spring when the outer ring portion secured to the armature is elastically deformed. However, there is a problem in which the ring-shaped leaf spring disclosed in the above publication does not have enough compressive force to deform the elastic member, because a length from the securing portion of the armature to the extending portion of the arm portion is long and the arm portion has a large deflection. For the sake of shortening the length of the arm portion, another securing portion may be disposed inwardly, but an increase in the number of the securing portion causes additional cost because of extra connecting means like rivets.
A plurality of three arm portions are provided in a circumferential direction of the leaf spring, and an elastic member is opposed to each arm portion. Thus, there is a problem in which the electromagnetic clutch needs a large number of parts and a large number of man-hours. Furthermore, the elastic member reduces the clutch operating noise only when the electromagnetic clutch is ON. It is necessary to reduce the operating noise when the electromagnetic clutch is OFF and the armature attracted to the drive-side rotation member is separated therefrom and returns to its original position.
In view of the above fact, an object of the present invention is to provide an electromagnetic clutch whose operating noise can be reduced at a low cost by using an elastic member which is better suited to a spring force of an attracted and separated leaf spring.
According to a first aspect of the present invention, an electromagnetic clutch comprises an electromagnetic coil (3) for generating an electromagnetic force when being energized, a drive-side rotation member (4) rotated by a driving source, an armature (5) attracted to the drive-side rotation member (4) in response to the electromagnetic force generated by the electromagnetic coil (3) to receive rotation of the drive-side rotation member (4), a driven-side rotation member (6) connected to a driven-side device (7), and a spring means (61). The spring means (61) couples the armature (5) to the driven-side rotation member (6) and supports the armature (5) such that the armature (5) is capable of being displaced toward the drive-side rotation member (4).
The electromagnetic clutch has a spring means (61) composed of a plate of a polygonal leaf spring (61). The leaf spring (61) comprises an outer ring portion (61c) connected to the armature (5), an attachment portion (61b) positioned inside the outer ring portion (61c) and connected to the driven-side rotation member (6). A connecting portion (61d) that connects between the outer ring portion (61c) and the attachment portion (61b), and a plurality of securing portions (62) of the armature (5) are disposed in a circumferential direction of the outer ring portion (61c). A plurality of first elastic members (67) are disposed at intermediate points of the plurality of securing portions (62) in the circumferential direction (around) of the outer ring portion (61c) to give an initial deflection to the leaf spring (61).
A second elastic member (66) is disposed between the leaf spring (61) and the drive-side rotation member (4) in an axial direction. The second elastic member (66) is elastically deformed between the leaf spring (61) and the driven-side rotation member (6) when the electromagnetic force generated by the electromagnetic coil (3) displaces the armature (5) toward the drive-side rotation member (4) in an axial direction and the armature (5) collides with the first elastic portions (67) to determine its axial position when the electromagnetic coil (3) is unenergized and the armature (5) is separated from the drive-side rotation member (4) to return to an original position.
According to the above aspect of the invention, when the clutch is actuated, namely when the leaf spring (61) connected to the armature (5) is displaced in the axial direction to the drive-side rotation member (4), the second elastic member (66) is elastically compressed between the leaf spring (61) and the driven-side rotation member (6) so that an elastic reaction force is generated in the second elastic member (66) in response to an increase in a displacement amount of the leaf spring (61). Since this elastic reaction force rapidly increases just before the armature (5) is attracted to the drive-side rotation member (4), the rapid increase in the elastic reaction force of the second elastic member (66) alleviates an impact produced when the armature (5) is attracted to the drive-side rotation member (4), and effects further reduction in the clutch operating noise.
On the other hand, when the clutch is OFF, namely when the armature (5) returns to the original, separate position by a spring force of the leaf spring (61), the armature (5) collides with the first elastic members (67) and determines an axial position thereof so that damping of the leaf spring (61) itself is alleviated and the clutch operating noise is reduced.
According to a second aspect of the invention the leaf spring (61) has the attachment portion (61b) formed in an approximate triangular shape, and has the connecting portions (61d) in the vicinity of the apexes of the triangular shape to connect with the outer ring portion (61c). The outer ring portion (61c) connected to the connecting portions (61d) is so formed in a polygonal shape as to have the largest outer dimensions.
According to the above second aspect, the leaf spring (61) of the present invention performs its spring function when the outer ring portion (61c) is connected to the armature (5) and the connecting portions (61d) are elastically deformed. Since the leaf spring (61) is formed in a polygonal shape in order to make an outer dimension of the outer ring portion (61c) connected to the connecting portions (61d) largest in size, the outer ring portion (61c) is large in size and a distance between fulcrums of the spring (spans) increases. Therefore, it is possible to reduce the spring force which is necessary to displace the armature (5) a predetermined amount.
According to a third aspect of the invention the leaf spring (61) is provided with arm portions (61e) inwardly extending from the outer ring portion (61c) in the vicinity of the securing portions (62). The second elastic member (66) is elastically deformed between the arm portions (61e) and the driven-side rotation member (6).
According to the third aspect, the arm portions (61e) for compressing the second elastic member (66) are provided in the vicinity of the plurality of securing portions (62) connected to the armature (5), so that the spring force is certainly transmitted from the securing portions (62) to the arm portions (61e) and the compressive force for compressing the second elastic member (66) increases. Thus, the clutch operating noise is reduced.
According to a fourth aspect of the invention, a length of the arm portion (61e) from the securing portion (62) to a tip of the arm portion (61e) is shorter than a predetermined length. According to the fourth aspect of the invention, an alleviation effect of the clutch operating noise depends on the compressive force of the arm portions (61e). Thus, restriction of the length from the securing portion (62) to a tip of the arm portion (61e) reduces the clutch operating noise. If the length exceeds the predetermined one, deflection of the arm portion (61e) increases, so the compressive force is not properly exerted.
According to a fifth aspect of the invention, the armature (5) is formed in an approximate ring shape, and the plurality of securing portions (62) are disposed at the approximate center of a radial width of the armature (5). Additionally, since the securing portions (62) are disposed at the approximate center of a radial width of the armature (5), the displacement amount of the armature (5) attracted to and separated from the drive-side rotation member (4) is certainly transmitted to the leaf spring (61). Therefore, it is possible to efficiently exert the electromagnetic force.
According to a sixth aspect of the invention, the second elastic member (66) with a plurality of approximate D-shaped elastic portions (66a) is so integrally formed as to be fitted in an outer periphery of the attachment flange (60b), and the second elastic member (66) disposed between the arm portions (61e) and the driven-side rotation member (6) is elastically deformed. Continuing, the integrally formed second elastic member (66) reduces the number of parts and the number of man-hours for related attachment processes, and results in a cost reduction.
According to a seventh aspect of the invention, the second elastic member (66) is integrally formed with the first elastic members (67) which are disposed at intermediate points of the elastic portions (66a) in the circumferential direction (around) and give an initial deflection to the leaf spring (61). Continuing with the seventh aspect, the first elastic members (67) integrally formed in the second elastic member (66) further reduce the number of parts and the number of man-hours for the attachment processes, and result in a cost reduction.
Further areas of applicability of the present invention will become apparent from the detailed description provided hereinafter. It should be understood that the detailed description and specific examples, while indicating the preferred embodiment of the invention, are intended for purposes of illustration only and are not intended to limit the scope of the invention.